Hydraulic fracturing

ABSTRACT

Hydraulic fracturing a subterranean formation with frac fluid, the hydraulic fracturing including complex shear fracturing of the subterranean formation. The technique includes determining an amount of the complex shear fracturing occurring, and adjusting operating parameters of the hydraulic fracturing to increase the complex shear fracturing occurring. The amount may consider fracture surface area. The adjusting may consider resonant frequency of the subterranean formation rock being fractured. The complex shear fracturing may assist with diffusion production. The techniques may include a non-transitory, computer-readable medium having instructions executable by a processor of a computing device to facilitate the aforementioned actions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityto U.S. patent application Ser. No. 17/188,728, filed on Mar. 1, 2021,which in turn claims the benefit of priority to U.S. Provisional PatentApplication Ser. No. 62/983,184, filed on Feb. 28, 2020. The entirecontents of each previous application are incorporated by referenceherein.

TECHNICAL FIELD

This disclosure relates to hydraulic-fracturing analysis and control.

BACKGROUND

Hydraulic fracturing is generally applied after a borehole is drilledand a cased wellbore formed. Hydraulic fracturing employs fluid andmaterial (e.g., proppant) to create or restore fractures in a geologicalformation in order to stimulate production from new and existing oil andgas wells. Hydraulic fracturing in the oil and gas industry may increasethe flow and recovery of oil and/or gas from a well. Natural gas orcrude oil may flow more easily up the well.

Operating wells may be subjected to hydraulic fracturing to remainoperating. Fracturing may allow for extended production in older oil andnatural gas fields. Hydraulic fracturing may also allow for the recoveryof oil and natural gas from formations that geologists once believedwere impossible to produce, such as tight shale formations.

Hydraulic fracturing in development of an oil-and-gas well may involveinjecting water, proppant, and chemicals under pressure through awellbore into a geological formation in the Earth crust. Thus, hydraulicfracturing (also called fracing or fracking) is a well-stimulationtechnique in which rock is fractured by a pressurized liquid. Thehigh-pressure injection of fracing fluid (also labeled as frackingfluid, frac fluid, etc.) into a wellbore generates cracks in thedeep-rock formations through which natural gas, petroleum, and brinewill flow more freely.

An example fracing fluid is primarily water containing sand or otherproppants. In some instances, water and proppant make up 98 to 99.5percent of the fluid by volume used in hydraulic fracturing. Inaddition, chemical additives may be incorporated in the water to alterviscosity. The formulation may vary depending on the well. In someexamples, the sand or other proppants may be suspended in the water withthe aid of viscosity increasing agents. Other chemical additives may beadded to the fracing fluid to reduce friction, such as in slickwater.Fracing jobs may direct completion hardware, proppant weights, and watervolumes to place sand as proppant in the fractures.

SUMMARY

An aspect of the present techniques relates to a method of hydraulicfracturing a subterranean formation, including injecting frac fluid andproppant through a wellbore into the subterranean formation. The methodincludes hydraulic fracturing the subterranean formation with the fracfluid. The hydraulic fracturing includes shear fracturing rock in thesubterranean formation. The method includes measuring pressureassociated with the hydraulic fracturing. The method includes receivingan indicator of an amount of the shear fracturing occurring per unittime. The method includes adjusting operating parameters of thehydraulic fracturing to increase the amount of shear fracturingoccurring per unit time. The adjusting of the operating parameters mayinvolve multiple adjustments of an operating parameter over time togoal-seek the shear fracturing to become super shear fracturing.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of the real-time fracing process and a well sitehaving a hydraulic fracturing system.

FIG. 2 is a diagram of a geological formation having fractures around awellbore.

FIG. 3 are representations associated with fracing-fluid liquid flowthrough fractures and with the presence (or lack thereof) of proppant.

FIG. 4 is a plot of an exemplary depiction of certain variables of thepresent hydraulic fracturing over time.

FIG. 5 is an output image of Fourier Transformed fracture harmonics overtime.

FIG. 6 are diagrammatical representations of shear fracturing and supershear fracturing.

FIG. 7 is a three-dimensional plot showing different fracture counts andtracer distances from wells, as fractures vary by geologic layer.

FIG. 8 is a diagrammatical representation of micro seismic eventscontained in rock bedding layers during hydraulic fracturing.

FIG. 9 are images depicting diffusion fluid behavior in fractured rockover a time sequence.

FIG. 10 is a plot over time for hydraulic fracturing of rock in asubterranean formation showing sum of surface area for shear fracturing,which is the sum of permeability enhancement for shear fracturing.

FIG. 11 is diagram of a computing system having a processor and memorystoring code executed by the processor to receive an indicator of theamount of shear fracturing during hydraulic fracturing.

FIG. 12 is a block diagram of a tangible, non-transitory,computer-readable medium that can facilitate analysis and control ofhydraulic fracturing.

DETAILED DESCRIPTION

The hydraulic fracturing process, when performed in real time at thesurface, may include at least four actions: 1) calibrate slurry rate tomatch pressure leak-off by adjusting slurry rate to track pressure; 2)adjust slurry proppant concentration to control leak-off so fluidpressure is converted to stress, thereby creating fractures; 3) adjustslurry rates, viscosity and concentrations as rocks change to goal seek(test various scenarios) to trigger (initiate) super (highlydestructive) shearing; 4) calculate the surface area (ft{circumflex over( )}2) during shear fracturing and the permeability (ft{circumflex over( )}2) during super shearing. Shear fracturing may increase fracturesurface area and cause higher well production rates. Shear fracturing(including super shearing) may increase permeability and recoveryfactors.

Embodiments of the present techniques relate to hydraulic fracturing asubterranean formation to promote complex shear fracturing of thesubterranean formation. The hydraulic fracturing includes injectingfracing fluid through a wellbore into the subterranean formation. Thefracing fluid may generally have proppant. The fracing fluid as injectedmay generate stress waves in the rock being fractured to advance theshear fracturing. The fracing fluid may initiate or trigger stress wavesthat then self-propagate. The presence of the injected proppant in theshear fractures can reduce leak-off of the fracing fluid into theformation and facilitate generation of stress in the rock via thefracing-fluid pressure.

Operating parameters of the hydraulic fracturing may be adjusted in realtime to goal seek to reach super shear fracturing. The operatingparameters adjusted may include, for example, flow rate of the fracingfluid, concentration (and size) of proppant (e.g., sand or manufacturedproducts) in the fracing fluid, and so on. The occurrence and magnitudeof the adjustments in the goal seeking to attain super shear fracturingmay take into account (or be in response to) measured variables ordetermined indicators of the hydraulic fracturing. A measured variableconsidered may be, for example, the pressure associated with thehydraulic fracturing. The pressure may be measured, for instance, at thewellhead or downhole. A determined (e.g., calculated) indicator that maybe received and evaluated can be, for example, an indicator of theamount of shear fracturing that is occurring. The indicator of theamount of shear fracturing may be an indicator of the number of shearfractures per time, surface area of the shear fractures being generatedper time, permeability enhancement associated with the shear fractures,permeability or permeability per time, effective permeability generatedor effective permeability generated per time, and so forth. Othermeasured variables and determined indicators are applicable.Permeability or effective permeability may be an indication of theactual measured permeability in subsequent production. Permeability maybe have units, for example, of Darcy or micro-Darcy and is generallyflow parameter. Flow can also be due to diffusion from the matrix rockinto shear fractures or super shear fractures.

In the goal seeking to implement super shear fracturing, the adjustmentsmay be an attempt to “fluidize” the rock layer(s) being subjected to thehydraulic fracturing to increase the amount of shear fracturing. Theadjustments may involve an effort for the applied stress waves (that mayself-propagate) to realize the resonant frequency of the rock toincrease the amount of shear fracturing.

The super shear fracturing may significantly increase fractured surfacearea and permeability enhancement as compared to typical shearfracturing or planar tensile fracturing. The super shear fracturing mayalso extend the fracturing into deeper regions of the geologicalformation from the wellbore. In some instances, the super shearfracturing may reach (connect to) natural fractures or expulsionfractures where hydrocarbon may flow, for example, by diffusion orcapillary flow. Diffusion is flow caused by differences in concentrationgradient. Other flow (e.g., all other flow) is caused by pressuregradients. In all, the super shear fracturing in comparison to typicalshear fracturing or simple tensile fracturing may: (1) increasefractured surface area that may increase hydrocarbon production ratefrom the geological formation; and (2) connect to natural fractures togive more fractured volume of the formation with enhanced permeabilityand increased hydrocarbon recovery by diffusion.

Embodiments of the present techniques may relate to hydraulic shearfracturing of a subterranean formation to reach super shear fracturing.Such may involve fluidizing rock and forming resonant stress waves inthe rock in the subterranean formation. Techniques that favor complex(shear) fracturing are disclosed in U.S. Pat. No. 10,711,604, which isincorporated herein by reference in its entirety for all purposes. Thosetechniques favor complex (shear) fracturing over simple (tensile)fracturing, and involve converting pressure to rock stress. Embodimentsherein may focus stress waves (e.g., as energy pulses) so that rock isalternately stressed and de-stressed in constructive waves that areadditive to rock destruction. Once these stress waves have beengenerated (initiated or triggered), the stress waves may then beself-propagating with typical input of frac fluid and proppant. Thus,once initiated, the stress waves may self-propagate in implementations.Constructive stress waves can cause rock destruction as the stress wavespass through geological layers of rock. The adjacent layers may bemechanically similar in certain instances. Each rock layer can have anatural harmonic frequency (e.g., unique for that rock layer) that maybe realized to trigger (initiate) super shear fracturing. Typically,laminated rocks (e.g., source rock shales) may be beneficial candidatesfor these techniques. When hydraulic fluid is injected under pressure,the rock can be effectively fluidized (floated). This may or may not bebecause the pressure is adequate to support enough of the weight ofoverlying overburden rock such that the rock can expand slightly, andcan be because capillary forces increase fluid penetration alonggeologic planes of weakness, such as bedding planes. Geologic mechanicallayers that shear fracture in response to stress waves or pulsed stresswaves may be production targets for unconventional reservoir production.

Initially in a hydraulic fracturing job, the flow rate of fracing fluidthat can be reasonably accepted into the geological formation can beestablished to generate shear fractures. The relationship offracing-fluid flow rate versus the pressure associated with thehydraulic fracturing may be calibrated. The flow rate may account forleak-off of the fracing fluid into the geological formation in theforming of the shear fractures in the formation. Then, proppant (e.g.,sand or other material) may be added to the fracing fluid to prevent orreduce leak-off of fracing fluid from the fractures into the formation.The proppant added may be small, such as 100 mesh or smaller (e.g., 140mesh or 200 mesh), such that the injected proppant may be conveyedtoward fracture tips. The presence of the proppant toward the fracturetips may provide resistance to fracing fluid flow (and reduce leak-off)to increase pressure in the fractures (e.g., provide a form ofbackpressure). The pressure may generate stress in the rock beingfractured. The fracing-fluid slurry having the proppant may beintroduced through the wellbore into the geological formation to reduceleak off and to convert pressure to stress. In goal seeking to realizesuper shear fracturing, the fracing-fluid flow rate and proppantconcentration may be adjusted to trigger (initiate) shear fracturing orsuper shear fracturing.

In certain embodiments, super shear fracturing may be defined as thegeneration of an obvious or significant slope increase in the sum ofshear fracturing events. The onset of shear fracturing and how definedor quantified may be related to the rock type and the particular fracingjob.

One or more indicators of the shear fracturing may be received,determined, or calculated. The fracture surface areas of the planartensile fractures and shear fractures may be calculated. The fracturesurface area of the shear fractures in the super shear fracturing may becalculated. The permeability enhancement by the super shear fracturingmay be calculated. These calculations calibrate the number of fracturesto production rates measured at individual stages and stimulatedreservoir volume (SRV) measured from post frac pressure declinecalculations.

FIG. 1 is a well site having a hydraulic fracturing system 100 thatemploys a fracing process with fracing slurry having fracing fluid 102(e.g., slickwater) and proppant 104. The fracing fluid 102 may be heldin a vessel(s). The fracing fluid 102 and proppant 104 may be stored invessels or containers and including on vehicles (e.g., trucks, skids,etc.) in certain examples. In some implementations, the fracing fluid102 is slick water which may be primarily water, such as 98.5% or moreby volume. The fracing fluid 102 can also be gel-based fluids. Thefracing fluid 102 can include polymers and surfactants. Other commonadditives may include hydrochloric acid, friction reducers, emulsionbreakers, emulsifiers, and do on. At the well site, the proppant 104 canbe provided from multiple railcars, hoppers, containers, or bins ofproppant of differing mesh size (particle size).

The system 100 includes control devices 106 and 108 for the fracingfluid 102 and the proppant 104, respectively to prosecute the fracingprocess that are actions to realize shear and super shear fracturing.The control device 106 may include pumps as motive devices (and also asmetering devices in some examples). The control device 106 for thefracing fluid 102 may also include a control valve in certain examples.The pumps may be, for example, positive displacement and arranged inseries and/or parallel. In some examples, the speed of the pumps may becontrolled to give desired flow rate of the fracing fluid 102. Theproppant control device 108 may include, for example, a blender, feeder(e.g., rotary feeder, etc.), conveying belt, metering device, and so on.A blender, for example, may be a solid blender that blends proppant 104of different mesh size. The proppant 104 may be added (e.g., viagravity) to a conduit conveying the fracing fluid 102 such as at asuction of a fracing fluid pump (e.g., of 106) to give a stream 110 thatenters the wellbore 112 for the hydraulic fracturing. Thus, the stream110 may be a slurry that is a combination of the fracing fluid 102 andproppant 104. The stream 110 may be labeled as fracing fluid or asfracing fluid having proppant. For instances when proppant 104 is notadded to the fracing fluid 102, the stream 110 entering the wellbore 112for the hydraulic fracturing may be the fracing fluid 102 withoutproppant 104.

The wellbore 112 may be formed through the Earth surface 114 into ageological formation in the Earth's crust. The source of fracing fluid102 and the source of proppant 104 may be disposed at the Earth surface114. The wellbore 112 may be vertical, horizontal, or deviated. Thewellbore 112 may be a cemented cased wellbore and have perforations forthe stream 110 to flow (injected) into the formation. Balls that seat inthe well, or other techniques, may also be utilized to control thefracing (fracturing) process.

The hydraulic fracturing system 100 may include a control system 116 todirect operation of the hydraulic fracturing system. The fracturingsystem 100 generally includes gauges or sensors to measure differentoperating parameters. For example, the system 100 may include a pressuresensor 118 disposed at a wellhead (not shown) of the wellbore, or in thesubsurface of the wellbore 112 to measure the wellhead and/or bottompressure during the hydraulic fracturing. In some implementations, thecontrol system 116 may receive the measured pressure data and may alsoconsider the wellhead pressure as the treating pressure of the hydraulicfracturing. The control system 116 may include a computing system toimplement techniques described herein associated with analysis andcontrol. The computing device may be disposed within the control system116. The computing device may instead be a field computer or remote. Thecontrol system 116 may include one or more controllers. The controlsystem 116 (and the computing device) can include a processor(s) 120,such as a central processing unit (CPU) or microprocessor, or cloudbased computing system. The control system 116 (and the computingdevice) can include memory 122 storing code (e.g., logics, instructions,etc.) executed by the processor 120. The memory 122 may include volatilememory, such as random access memory (RAM), cache, cloud computing, etc.The memory 122 can include nonvolatile memory, such as a hard drive,read only memory (ROM), solid state drives, or cloud servers, etc.

Hydraulic fracturing may create new fractures in the rock in thegeological formation, as well as increase the size, extent, andconnectivity of existing fractures and bedding planes in the geologicalformation. The producing formation is fractured open via hydraulicpressure. Then, proppants 104 (propping agents) are pumped into the oilwell with fracing fluid 102 to hold the fractures or fissures open sothat energy (pressure) can be applied (e.g., via pumped fracing fluid)into the formation and converted to stress to enhance the breaking ofthe rock. Hydraulic fracturing is generally employed in low-permeabilityrocks, such as tight sandstone, shale, and some coal beds, to increasecrude oil or gas flow to a well from petroleum-bearing rock formations.A beneficial application may be horizontal wellbores in low-permeabilitygeological formations having hydrocarbons, such as natural gas, crudeoil, etc. Massive hydraulic fracturing or high-volume hydraulicfracturing may be applied to gas or oil-saturated formations with lowpermeability (e.g., less than 0.1 millidarcy) and often in the nanodarcyrange (e.g., less than 1 microdarcy) of permeability. At very lowpermeability, such as less than 1 microdarcy or less than 0.1microdarcy, diffusion production may become more important or moresignificant contribution.

Some hydraulic fracturing generally accepts whatever fracture typesdevelop. In contrast, embodiments herein generate hydraulic fracturespossible by measuring the harmonic frequency of geo-mechanical layersand adjusting hydraulic fracing parameters (operating variables) tocreate constructive interference. A measure of stress waves may classifydifferent degrees of shear fracturing. Embodiments may measure or reachthe natural harmonic frequency of different geologic layers. Increasedshear fracturing may be realized at this frequency giving significantlyincreased rock destruction. Stress patterns may identify shearfracturing by the length of time (period) to initiate and propagate eachtype of fracturing (e.g., shear fracturing versus planar tensilefracturing). The fracing slurry flow rate and proppant concentration ofsand-fluid slurries may be adjusted to trigger the onset of significantshear fracturing (e.g., including laminated-rock shear fracturing) foreach stage having particular geo-mechanical layer(s). The number ofshear fractures or extent of shear fracturing may be counted ordetermined in each hydraulic-fracturing stage to select rock forcompletion and production.

The current present techniques may provide for real-time(second-by-second) control of types of fractures that form to createincrease fracture surface-area and well productivity. The techniques mayaccount for efficient utilization of injected water and sand.Hydrocarbon recovery may be increased, well spacing may be improved,field developments may be focused in the desired pay zones, and reducedwell declines may be achieved with diffusion production.

Initially for a fracing job, the techniques may generally identify thetype of rock to be fractured in each stage. The rock may be classifiedby a combination of stratigraphic and mechanical bedding, such asmassive, laminated, expulsion fractured, etc. The block size may also beconsidered, as discussed below. The techniques may involve designing thecompletion for working proppant concentration, which will convertpressure (energy) to stress. The techniques may including actions suchas to: (1) fluidize rock by adjusting fluid rates and resulting pressurechanges in real time; (2) increase fluid rates to increase stress andobserved pressure; and (3) decrease fluid rates to cause rock failureand decrease pressure. Embodiments may guide the separation of measuredand guidance pressures in real time including to cause pressure curvesto drift together upward (increasing stress) or drift apart downward(increased fracturing). The guidance pressure may be determined ordefined as a calculated pressure that is computed by equations orartificial intelligence, from a nearby stage with treating pressuremeasured in similar rock, proppant, and fluids. Or by utilizing advanceddeep learning neural nets with Bayesian statistics that displaystatistical uncertainty through real time (second-by-second) or delayedtime, in fracturing stages.

Fracture systems may be dilated with fluid that is laden with proppantin balanced systems. Relatively small adjustments in fluid rate mayallow fractures to grow. Relatively small adjustments in fluid rate maymore effectively facilitate fractures to fill with proppant. Generally,no two fracture systems are the same and thus design or models ofoptimal completions may be problematic. To compensate for ever changingfracture systems, fractures may be measured and classified as shear ortensile and can be counted, e.g., within 15-20 seconds or less from thetime they are formed. This may facilitate frac engineers to focus onincrease or decrease in fracing fluid rates, proppant concentration inthe fracing fluid, proppant size, and fluid viscosity accordingly. Oncethe rock being fractured is effectively fluidized (floated) becausepressure is high enough to penetrate rock, stress waves within the rockvolume may become self-propagating. It is observed that frac fluidpenetrates rock at pressures below those needed to lift overburden rock.

Stress waves exhibit different frequencies which can be measured andstimulated to be additive for triggering wave trains that may extend fortens or thousands of seconds. The amount of shear fracturing can bedefined as shear fracturing or super shear fracturing.

FIG. 2 is a geological formation 200 having fractures around a wellbore202. Fractures may begin vertical along, or perpendicular to wells. Thefractures may grow in exiting fractures within bedding layers. Thewellbore 202 may have perforations 204 for injection of fracing fluidinto the geological formation 200. In the illustrated embodiment, thewellbore 202 is a horizontal wellbore. The fractures may includefractures along vertical (or near vertical) fracture planes 206 withrespect to the wellbore 202. The vertical planes 206 may include avertical plane (or near vertical plane) that is generally perpendicularto the longitudinal length of the wellbore 202 and may include avertical plane that is parallel (in-line) with the longitudinal lengthof the wellbore 202. In other words, the fractures may begin verticalperpendicular to the wellbore 202 and also may begin vertical along thewellbore 202. The fractures may grow into existing fractures withinbedding layers. These fractures 208 (shear fractures and/or connectedexisting fractures) may be in a horizontal bedding layer(s) 210. Thefracture tips of the fractures 208 (or a portion of each fracture 208toward or near the fracture tip) may receive proppant. The proppant maybe fine sand or other material (e.g., generally 100 mesh or less) sothat the proppant may reach further into the fractures 208.

FIG. 3 are representations 300 associated with fracing-fluid liquid flowthrough fractures and the presence (or lack thereof) of proppant (andproppant size). Small fractures are generally closer together and stressrock more than larger fractures. There are typically many more smallfractures than large fractures. The liquid in the fracing fluid may beprimarily water. The diagrammatical representation 302 is for flow 306of the fracing-fluid liquid through fractures 304 with no proppant.Therefore, water (liquid) flow is generally unrestricted (there may below restriction due to lack of proppant limiting fluid flow) and thuslower stress is generated. The rock can be characterized as notefficiently fractured.

The representation 308 is for flow 310 of fracing fluid throughfractures 312 with 40/70 mesh proppant 314. The water (liquid) flow isrestricted by the proppant 314 and therefore stress 316 is generated onthe rock being fractured. The rock can be characterized as somewhatstressed and not optimally fractured because fluid can generally leakthrough 40/70 and coarser sands more easily than 100 mesh and smallerparticle sand and smaller proppants.

The representation 318 is for flow 320 of fracing fluid throughfractures 322 with 100 mesh and smaller proppant 324. The water (liquid)flow is restricted by the proppant 324 and therefore optimal orbeneficial (increased and decreased) stress 326 is generated in the rockbeing fractured. The rock may be characterized as highly stressed andhighly fractured in some examples. In other words, the smaller 100 mesh(or finer) proppant 324 may be able penetrate further into the fracturesthan the 40/70 mesh (or larger) proppant. In certain instances, thesmaller 100 mesh (or even smaller mesh) proppant 324 can also give amore densely fractured formation, with more fractures per barrel ofwater.

The small fractures 322 are closer together than larger fractures andmay generally stress the rock more than large fractures farther apart.There may be a much greater amount of small shear fractures than largeshear or tensile fractures, making better connections to naturalexpulsion fractures caused by oil or gas expansion.

FIG. 4 is a plot 400 of exemplary depiction of certain variables of thepresent hydraulic fracturing over time 401 (seconds). Real-timeadjustments are made to frac fluid (water) rate and proppant (sand)size/concentration. Small changes in frac fluid rate or sandsize/concentration can sometimes dramatically affect shearing.

Indications of the amount (e.g., number or count, surface area, etc.)per time 401 of both tensile fractures 402 and shear fractures 404 aregiven in plot 400. The indicator (curve) of shear fractures 404 may bethe fracture count of shear fractures per time (e.g., per second). Theindicator may be the fracture surface area generated through time. Theindicator may also include or account for added permeability (orincreased recovery) due to super shear fracturing and concentrationgradient (diffusion) production.

Embodiments may receive the indicator of shear fractures 404 and makeadjustments to operating variables accordingly. Multiple implementationsfor determining an indicator of shear fractures 404 are applicable. Thedetermination of the indicator may be based on pressure associated withthe hydraulic fracturing. The determination of the indicator (of shearfractures 406 per time) may be based, for instance, on a regression orneural network that weights fracing-fluid flow rate, proppantconcentration, fracing fluid properties (e.g., viscosity), rockproperties, and other factors. In some instances, the shear-fracturesurface area may be characterized as the area under the sum of curve406. In implementations, the determination of the indicator may be basedon pressure derivatives of the hydraulic fracturing, and so on. Thedetermination or calculation may be performed with neural networks,machine learning, artificial intelligence, or computer code withequations, or any combinations thereof. The indicator may be based onease at which the proppant is placed in the complex shear fractures atlower rates than to place proppant in tensile fractures, the increasedproductivity of shear fractured wells, and observed requirement for lesswater to place the same amount of proppant in fracture systems withgreater surface area. The indicator may have units of number offractures or area (e.g., square feet).

The pressure 406 (e.g., in pounds per square inch gauge or psig)associated with the hydraulic fracturing is plotted over the time 401.The pressure 406 may be wellhead pressure, downhole pressure, acalculated pressure (e.g., correlative with hydraulics), or somecombination thereof. The water 408 curve is the flow rate of the fracingfluid. The units of the flow rate can be, for example, barrels perminute (bpm), cubic meters per minute, or gallons per minute (gpm). Theliquid in the fracing fluid may be primarily water (e.g., greater than98% by volume) and therefore the simplified label of “water.” The water408 curve may be a slurry rate (total flow rate of the fracing fluidhaving both liquid and solids) when proppant is added to the fracingfluid.

Lastly, the sand/proppant concentration 410 (e.g., weight percent orvolume percent) in the fracing fluid is plotted. The proppant may be,for example, 40/70 mesh or smaller, 100 mesh or smaller, or 200 mesh. Insome examples, the proppant concentration 410 may be based on the flowrate of fracing fluid and the addition rate of the proppant. In otherexamples, the proppant concentration 410 may be indicated based ondensity of the fracing fluid.

As indicated by the plot 400, real-time adjustments may be made to thefracing fluid flow rate 408 and to the proppant concentration 410.Relatively small changes in fracing-fluid flow rate and proppantconcentration can significantly affect the amount of shear fracturingthat occurs.

The fracing fluid may generally have proppant (e.g., proppant at 40/70mesh, 100 mesh, or 200 mesh) that is conveyed to the shear fractures.The presence of the proppant in the shear fractures may reduce leak-offof the injected fracing fluid through the shear fractures into thegeological formation and thus facilitate conversion of pressure tostress.

FIG. 5 is an output image 500 of Fourier Transformed fractured harmonicsover time 502. The image 500 is embedded on a plot 504 over time 502 ofhydraulic-fracturing variables including an indicator 506 of the amountof shear fracturing per unit time. A trigger is indicated as beginning508 and ending 510.

FIG. 6 are diagrammatical representations 600 of shear fracturing 602and super shear fracturing 604. The dendritic growth for the fractures606 is greater for the super shear fracturing 604 than the shearfracturing 602. Shearing stress waves 608, 610 are applied and realizedin the rock being fractured.

FIG. 7 is a three-dimensional plot 700. The X axis is distance along thewells measured in feet. The Y axis is distance in front of and behindthe wells in feet. The Z axis is the true vertical depth below sealevel. The plot 700 indicates that fracture counts of the shearfracturing are adjusted to oil tracer concentration to providebeneficial well spacing. Depicted in the plot 700 are fracture counts(lines) per stage and the approximate distances hydraulic fracturesextend from the wells. A different oil tracer is injected in each stage.Also depicted is oil tracer concentration measured by stage (withdifferent line types).

FIG. 8 is a diagrammatical representation 800 of micro seismic eventscontained in rock bedding layers during hydraulic fracturing. Microseismic events are typically in clusters. Dark shading indicates themost events.

Beds have many shear fractures. There are only a few tensile (vertical)fractures observed. The plot 802 gives over time the surface pressure,fracing-fluid flow rate, and fracing-fluid proppant concentration for afracturing stage. The image 804 is the frequency (hertz) of thefractures over the same time scale as the plot 802. The micro seismicevents may occur in layers with common frequency caused by similar rockbreaking frequency. Dark shades indicate few fracturing events. Lightershades indicate large numbers of micro seismic events. The Y scale onthe lower portion of plot 804 is frequency in hertz (Hz) and notnecessarily matched to depth for this example.

FIG. 9 are images 900 that depict diffusion fluid flow behavior infractured rock over a time sequence of Time A, Time B, and Time C. Fluidmoves through core by diffusion in minutes at Time C. Fluid saturationthrough core in fractures took about 1 hour at Time A. Diffusion can bea major production mechanism. Fluid saturation (concentration gradients)were measured via neutron tomography tracks water saturation (darkershading in center) advancing through core in fractures and rock layers.Water began filling at Time A and filled the rock sample completely atTime C. This filling process took about one hour. After fluid saturationat Time C, fluids moved from top to bottom in the rock sample bydiffusion in about one minute. As an analogy, diffusion is whatexchanges oxygen and carbon dioxide in lungs. Diffusion can be veryrapid and efficient once established.

FIG. 10 is a plot 1000 over time 1002 (seconds) for hydraulic fracturingof rock in a subterranean formation. Block size (1004) may greatlyincrease shearing when block size is small. Block size can be scaled,for example, from 1 to 100 feet. Blocks greater than 30 feet per sidemay generally have low recovery and diffusion flow. Blocks smaller than30 feet generally have high recovery and diffusion flow. The curve 1004is an indicator of the rock block sizes resulting from shear fracturing.Large rock blocks (high values) might represent blocks greater than 30feet on a side. Small rock blocks (low values) may represent rock blocksas small (e.g., analogous as Rubik's cubes). In some implementations, ablock size curve 1024 on the real-time plot may be the inverse orproportional to the inverse of frequency of the fractures. The frequencyvalue may be or related to, for example, average derivative pressurecalculated over time. Other configurations are applicable. In general insome embodiments, for “block size” the more breaks per time interval,the smaller the rock in the rock breakage.

The shear fracturing includes an initial region 1006 of shear fracturing(beginning about the time of sand input), a subsequent region 1008 ofincreased shear fracturing that persists for about 2000 seconds, and aregion 1010 of super shear fracturing that persists for about 4000seconds. Curves depicted in the plot 1000 include fracing-fluid slurryrate 1012, fracing-fluid proppant concentration 1014, pressure 1016measured at the wellhead of the wellbore through which the fracing fluidis applied, and a guidance pressure 1018. In this example, the proppantconcentration 1014 is based on the density of the fracing fluid. Theportion 1014A shows when acid was added to the fracing fluid. Theguidance pressure 1018 are pressure values computed by equations orneural networks, or artificial intelligence for the rock type fracturedwith 100 mesh or finer sand. Guidance pressure is used to recommendtreatment pressures. When measured pressure exceeds guidance pressure,such might indicate that sand is over filling fractures. When measuredpressure is less than guidance pressure, such might indicate that fluidis leaking from the fractures too quickly to generate stress. A curvefor the sum 1020 of shear fracture surface area is given. In the region1010 of super shear fracturing, a branch of the sum 1022 of fracturingsurface additionally includes an indication of enhanced permeability(also in square feet) due to the shear fracturing that may increasetotal hydrocarbon recovery and reduce well production declines from thatwell in the geological formation.

As mentioned, a block size 1024 curve is depicted. The block size 1024generally decreases through the hydraulic fracturing. The block size maybe defined as the relative sizes of rock blocks that are created byhydraulic fracturing. Small blocks generally fracture with greaterfracture density and efficiency.

Block size may be inversely proportional to breakage frequency indicatedby measured pressure and the aforementioned calculations via equationsor neural networks. The more frequent the measured fracture breaks, thesmaller the block size. There is generally increase in shear fracturingwhen block size decreases. Frac-fluid injection and proppant (sand)concentration may be additionally considered. What can make block sizesignificant is that the number of pre-existing expulsion (micro)fractures may dominate hydraulic fracturing behavior. Block size may becorrelative with and utilized to indicate the number of fractures andpresence of shear fracturing or super shear fracturing. Block size alsobe calibrated to hydrocarbon production performance.

As mentioned, techniques are described in U.S. Pat. No. 10,711,604 tocreate more complex (shear) fractures and fewer simple (tensile)fractures by efficiently converting pressure to rock stress. Embodimentsof the present techniques may improve on this earlier work by (1)creating a range of small through larger hydraulic fractures that aresand filled and connected to hydrocarbon-filled pores and small naturalfractures where hydrocarbons move by diffusion (concentration gradientas well as by pressure gradient), and (2) focusing stress waves whichalternately stress and de-stress rocks causing significant constructiveshear waves of rock destruction. Once capillary fluid flow systems areconnected to hydraulic fractures, better than expected production andrecovery can result. In human circulatory systems, diffusion dominatesin small blood vessels and Darcy flow dominates in larger blood vessels.In reservoirs, pores and natural expulsion fractures exhibit capillaryflow and proppant packed hydraulic fracture have Darcy flow. Proppantsized by sieving may be utilized to systematically stress pores, naturalmicro fractures and laminations to provide proppant filled connectionsto producing oil and gas wells. Hydrocarbons trapped in tight matrixrocks may be released by breaking the rock into the small pieces. Thefracture dilation, proppant filling, rock stressing and rock failuremechanisms may be further enhanced by “fluidizing” the rock mass.Fluidization may be caused by maintaining pore fluid pressure aboveoverburden pressure to enhance rock destruction. This may be implementedby (1) increasing or dropping fluid pressure by filling or drainingfluid surrounding rock, and (2) increasing pore pressure to slip rocklaminae like disks on an air-hockey table.

The techniques may employ real-time (e.g., second-by-second) measures ofpressure or delayed 15-30 seconds measures of pressure) to observestress waves and maintain the forces of fracture dilation and closure inbalance, as proppant slurry fills the fractures. The maintainedpressure-rate balance that propagates stress waves which trigger(initiate) significant shear fracturing or the greater super shearfracturing can be triggered with small (˜0.5 to 1.0 bpm) changes infracing-fluid flow rate. Super shearing is a grade of greater shearfracturing. Geologic mechanical layers which exhibit stress associatedwith super shear fracturing can be in patterns that can be analyzed withFourier transforms to characterize dominant frequencies at which rockdestruction occurs. This knowledge may facilitate tuning of frac-fluidrates and proppant concentrations to increase fracture counts specificfor different geology (block sizes).

Aspects may be for real-time control of fracturing, which facilitatesfracture numbers and types to be observed as injection rates andproppant concentrations are adjusted. Embodiments may measure thenatural harmonic frequency at which different geologic layers fracturewith greater rock destruction. The number of fractures counted in eachstage may utilized as a variable to select the better rock forcompletion and production.

Certain embodiments may fluidize rock and adjust proppant-fluid slurriesto trigger the onset of super shear fracturing for each stage with theparticular unique geo-mechanical layer(s) of each stage. Someimplementations may generate laminated rock shear fracturing includingsuper shear fracturing by changing fluid pressure up or down. Rockssurrounded by fluid may be stressed by higher fluid rates andde-stressed with lower rates. Stress patterns are developed to identifyshear fracturing and super shear fracturing by the length of time(period) to initiate and propagate the fracturing.

Embodiments may utilize different sizes of proppant to invade and stressdifferent sizes of natural pores and micro expulsion fractures toconnect natural fluid diffusion networks to proppant-filled fracturesthat flow by Darcy (pressure drop) physics. Production rates may bepredicted from stimulated reservoir volumes (SRV's) that are shearfractured and filled with 40/70, 100, and 200 mesh or other smallproppants. Different proppant sizes may effectively connectdifferent-sized capillary flow networks to different-sized hydraulicfractures packed with proppant.

The discussion now turns to a rock stress curve. Pressure measurementsmay respond to fracing-fluid slurry rate, fracing-fluid proppantconcentration, fracing fluids and rock stress changes. This can bereduced, through calculation, to a rock stress curve. By calculating thefrequency spectrum (via fast Fourier transform or FFT) of this rockstress curve, the dominant frequencies of the rock breakage can bemonitored and recorded. Depending upon the slurry paths through theformation (reservoir) bedding planes, both vertical (or near vertical)and horizontal (or near horizontal), the shale (or low permeabilityrock) may break at measurable discrete frequencies that can be monitoredfrom the calculated rock stress curve. Analysis of these frequenciesrecorded in the frequency spectrum may provide a pattern (e.g., a uniquepattern) that defines how the rock is breaking. Utilizing patternrecognition, the frequency data may be categorized to determine thehomogeneity and/or heterogeneity of the rock lamination that isfracturing, as well as possible bed thicknesses and the position of bedsinvaded by slurry. These patterns can be input to a database and vianeural net and machine learning correlated with production data todetermine the level of productivity, via stimulated reservoir volume, ofeach frequency pattern. Information analyzed may include at leastgeographic location, basin, stratigraphic interval, rock character, rocktype, depth, completion fluids, proppant types and amounts, rates ofinjection, timing, delays, and patterns of fluid, proppant and chemicalinjection.

The correlation of frequency patterns, fracture types, fracture size,fracture number and rock block size, with other geologic andgeo-mechanical data (via the above-mentioned analyses) may yield designcurves (slurry rate, proppant concentration, block size, etc.) to beemployed for optimum stimulated reservoir volumes. This, in turn, mayincrease or give a beneficial production profile of each stage of eachwell, and also provides parameters to compute beneficial well spacingfor each pad. However, because design curves may be based on statisticalanalysis, the techniques can be augmented by utilizing the feedbackinformation from real-time data collection and analysis. Real-timefeedback from reservoir rock stress response, which may be determined orcalculated, can provided recommended or suggested real-timemodifications to the design curves to evaluate the degree of success ofcurve modifications. This continuous feedback loop, while the stage isbeing fractured, may yield beneficial completion settings available forthe current well/stage location and rock properties.

An embodiment is a method of hydraulic fracturing a subterraneanformation, including: injecting frac fluid comprising slurry through awellbore into the subterranean formation; measuring pressure associatedwith the hydraulic fracturing; adjusting slurry rate of the frac fluidto promote shear fracturing of rock in the subterranean formation,wherein the slurry rate comprises flow rate of the frac fluid with theproppant; and developing, via a processor, a rock stress curvecorrelative with the pressure, the slurry rate, a concentration of theproppant in the fracing fluid, and observed stress of the rock. Thestress in the rock may be indicated by the indicator of the amount ofshear fracturing e.g., by cumulative shear fracture count curve orshear-fracture surface-area curves that are generated in real time orsubstantially real time.

The method may include calculating (e.g., by Fourier transform, FFT,etc.) via the processor a frequency spectrum of the rock stress curve,wherein dominant frequencies of the frequency spectrum are indicative ofbreakage of layers of the rock. The method may include monitoring andrecording the dominant frequencies. The rock may break at discretefrequencies indicated via a frequency spectrum of the rock stress curve,wherein the discrete frequencies are measurable. The discretefrequencies may be correlative with a direction of a flow path of thefracing fluid through a bedding plane, or other plane of weakness in thesubterranean formation. A pattern of the discrete frequencies on thefrequency spectrum may be indicative of behavior of breaking of the rockcomprising the shear fracturing. The method may include categorizingfrequency data of the discrete frequencies via pattern recognition todetermine homogeneity and heterogeneity or the number of layers beingfractured.

The method may include categorizing frequency data of the discretefrequencies via pattern recognition to indicate a bed thickness of therock and a number of beds of the rock invaded by the fracing fluid. Inparticular implementations, the method may include to characterize thestages for production forecasting from the relative amounts of proppantpumped in each stage or from the frequency patterns that describe eachstage, or base on other factor. In the example of 200 mesh proppant, thestimulated 200 mesh volume (SRV) may be calculated based on the amount200 mesh proppant in certain instances. SRV's can be computed for eachof the proppants placed. Reservoir engineers may desire the SRV's fromeach stage.

FIG. 11 is a computing system 1100 having a processor 1102 and memory1104 storing code 1106 (e.g., logic, instructions, etc.) executed by theprocessor 1102. The computing system 1100 may be single computing deviceor a computer, a server, a desktop, a laptop, multiple computing devicesor nodes, a distributed computing system, control system, and the like.The computing system 1100 may be local (at the wellbore or remote fromthe wellbore. Indeed, the computing system may represent multiplecomputing systems or devices across separate geographical locations. Thecomputing system may be a component of a control system (e.g., 116 inFIG. 1 ). The processor 102 may be one or more processors, and may haveone or more cores. The hardware processor(s) 102 may include amicroprocessor, a central processing unit (CPU), graphic processing unit(GPU), or other circuitry. The memory 1104 may include volatile memory(e.g., cache, random access memory or RAM, etc.), nonvolatile memory(e.g., hard drive, solid-state drive, read-only memory or ROM, etc.),and firmware, and the like.

In operation, the computing system 1100 may receive measured pressuredata originating from a pressure sensor measuring wellhead or bottomhole pressure and also receive data from other sensors and controllers.The code 1106 may include an analyzer or analysis logic and a neuralnetwork when executed that directs the processor 1102 to receive,determine, calculate, or utilize an indicator of the amount of shearfracturing, a guidance pressure, and a rock stress curve or othercurves. The code 1106 may include an adjuster or controller which maygive instructions when executed that direct the processor 1102 tospecify a set point or adjust an operating parameter of the hydraulicfracturing system. The computing system 1100 is unconventional, forexample, in that the computer can utilize the indicator of shearfracturing and also specify adjustments of the hydraulic fracturing toincrease or advance shear fracturing. In this context, the computer isinnovative with respective to accuracy and speed (real time). Inaddition, the technology of hydraulic fracturing is improved. Further,this innovative computing system results in increased production ofhydrocarbon (e.g., crude oil and natural gas) from a well.

FIG. 12 is a block diagram depicting a tangible, non-transitory,computer (machine) readable medium 1200 to facilitate analysis andcontrol of hydraulic fracturing. The computer-readable medium 1200 maybe accessed by a processor 1202 over a computer interconnect 1204. Theprocessor 1202 may be a controller, a control system processor, acontroller processor, a computing system processor, a server processor,a compute-node processor, a workstation processor, adistributed-computing system processor, a remote computing deviceprocessor, or other processor. The tangible, non-transitorycomputer-readable medium 1200 may include executable instructions orcode to direct the processor 1202 to perform the operations of thetechniques described herein, such as to receive, determine, calculate,or utilize an indicator of the amount of shear fracturing, a guidancepressure, and a rock stress curve or other curves, and in some examples,adjust a controller or specify a set point for operation of a hydraulicfracturing system. The various executed code components discussed hereinmay be stored on the tangible, non-transitory computer-readable medium1200, as indicated in FIG. 12 . For example, an analysis code 1206 mayinclude executable instructions to direct the processor 1202 to as toreceive, determine, calculate, or utilize an indicator of the amount ofshear fracturing, a guidance pressure, and a rock stress curve or othercurves. Adjust code 1208 may include executable instructions to directthe processor to specify a set point or adjust an operating parameter ofthe hydraulic fracturing system. It should be understood that any numberof additional executable code components not shown in FIG. 12 may beincluded within the tangible non-transitory computer-readable medium1200 depending on the application.

An aspect of the present techniques relates to a hydraulic fracturingsystem including a pump(s) to inject fracing fluids and a blender(s) tovary proppants and fluid viscosities with pump rates through a wellboreinto a geological formation for hydraulic fracturing of the geologicalformation. The system includes a pressure sensor to measure pressureassociated with the hydraulic fracturing. The pressure sensor orpressure gauge may be at the wellhead of the wellbore or lowereddownhole into the wellbore, or be two pressure sensors with a pressuresensor disposed at each location, respectively. Again, the pressuresensors may include pressure gauges. Another aspect of the presenttechniques may relate to computer-facilitated or computer-guidedimplementation of real-time shear fracturing including analyses withneural networks, machine learning, artificial intelligence, or computercode with equations, or any combinations thereof.

The shear fracturing may generally be high surface-area shearfracturing. Complex shear fractures (or shear fractures) may be definedas fractures that are not simple planar tensile fractures. A planarfracture may be labeled as a tensile fracture or a planar tensilefracture, and the like. Shear fractures generally collectively have highsurface area relative to a planar tensile fracture system. Shearfractures may be small shear fractures that collectively give highsurface area including greater surface area than a single planarfracture. Thus, again, complex shear fracturing may be characterized ashigh surface-area shear fracturing. Complex shear fracturing may give alarge number of shear fractures or fracture branches (e.g., in alocalized volume) and in which the shear fractures can be very small.While the shear fractures may be referred to as complex shear fracturesdue to their formation via complex shear fracturing, the shear fracturesmay include simple shear fractures. Moreover, while complex shearfracturing may be referred to as giving high surface area, an individualor single shear fracture or branch may have less surface area than asingle planar tensile fracture. However, a shear fracture may becharacterized as dendritic and with many branches. Whether such afracture formation is viewed as a shear fracture or shear fractures,such a branching shear fracture or shear fracture event may originatewith (or be associated with) a stress event such as the relieving ofaccumulated stress. Hydraulic fracturing produces both tensile and shearfractures—both may be measured and counted to determine fractureefficiency. Indeed, hydraulic fracturing can include both shearfracturing and tensile fracturing. The presence of shear fracturing canbe determined. The presence of tensile fracturing can be determined.Permeability or effective permeability of the fractured formation may becorrelative (e.g., directly proportional) with the dendritic complexityand abundancy of the shear fracturing or shear fractures includingformed shear micro-fractures.

An embodiment is a method of hydraulic fracturing a subterraneanformation including to count number and types of fractures created inreal time. The method includes injecting a frac slurry comprising fracfluid and proppant through a wellbore into the subterranean formation,and hydraulic fracturing the subterranean formation with the fracslurry, the hydraulic fracturing including shear fracturing rock in thesubterranean formation. The method includes observing change in fracturecounts with changes in the proppant size, proppant concentration in thefrac slurry, and block size in the subterranean formation beinghydraulically fractured. The method includes measuring pressureassociated with the hydraulic fracturing, receiving an indicator of anamount of the shear fracturing occurring per unit time, and adjustingoperating parameters of the hydraulic fracturing in real time toincrease the amount of shear fracturing occurring per unit time. Theadjusting of the operating parameters may involve observing real-timeresponses of numbers of shear fractures over time to achieve shearfracturing and to perform goal seeking to give super shear fracturing,wherein the operating parameters comprise fluid viscosity of the fracfluid, flow rate of the frac slurry, block size and the proppantconcentration. The super shear fracturing may involve selection of rocklayers in stages, so that successfully super sheared zones from onestage can have processes repeated to achieve successful shear fracturingin other stages with similar or different rock.

An amount of hydraulic fracturing may be a fracture count that is anumber of shear and tensile fractures. An amount of hydraulic fracturingmay be surface area of shear and tensile fracturing, where the surfacearea gives hydrocarbon production by concentration gradients ordiffusion, and that leads to both higher wells rates and hydrocarbonrecoveries. An amount of hydraulic fracturing is permeability of supershear fractures, which generates higher production rates from pressuredrops in fractures generated in the shear fracturing including supershear fracturing. The shear fracturing may include an amount of supershear fracturing that is enhanced permeability of the geologicalformation due to the super shear fracturing that will give increasedtotal diffusion recovery of hydrocarbon from the geological formation.The method may include triggering stress waves in the rock with the fracslurry, wherein the stress waves are self-propagating and includeconstructively interfering stress waves.

The operating parameters adjusted in real time include flow rate of thefrac slurry. Adjusting the flow rate may be increasing the flow rate,wherein increasing the flow rate increases the pressure and increasesstress in the rock. Adjusting the flow rate may be decreasing the flowrate, wherein decreasing the flow rate decreases the pressure andreduces stress in the rock. Adjusting the flow rate may includeadjusting the flow rate in response to stress patterns in the rock toseek and create resonant frequency of fracturing. Adjusting the flowrate may generate energy pulses so that the rock is alternately stressedand de-stressed in constructive stress waves that are additive todestruction the rock comprising the shear fracturing. Adjusting the flowrate may give failure in the rock contributing to the shear fracturing.Adjusting the flow rate may include adjusting to a flow rate at whichthe laminations of the rock are fluidized with pressure that penetratesbeds at pressures below those required to support weight of overlyingrock. The pressure supporting the weight of the overlying rock mayfacilitate the frac fluid penetration of bedding of the rock, sufficientto flex the rock to cause beds to slip analogous to a folded card deck.The method may include maintaining the pressure below a threshold suchthat planar tensile fracturing does not occur.

The operating parameters adjusted may include concentration of theproppant in the frac fluid. Adjusting operating parameters may includeadjusting an amount of the proppant placed in shear fractures generatedin the shear fracturing, wherein the proppant comprises sand or othermaterial of a size to enter small fractures and control leak-off andincrease stress. The method may include fluidizing the rock which mayinvolve the pressure not exceeding weight of overlying overburden rock,because rock planes of weakness take fluid below the overburdenpressure.

Adjusting the operating parameters may generate stress waves in therock. In this context, adjusting the operating parameters may involvegoal-seeking for the stress waves to propagate at resonant stressfrequency of the rock. Adjusting the operating parameters may initiatestress waves in the rock, and wherein the stress waves areself-propagating after initiation. Measuring the pressure may involvereal time measurements of the pressure to observe stress waves in therock. In this context, the stress waves may have a frequency equal tothe resonant stress frequency, and wherein the resonant stress frequencycomprises a natural harmonic frequency at which the rock will vibratewith the stress waves. The proppant in the frac fluid may facilitatetransfer of pressure of the frac fluid to the rock as stress.

The method may include specifying a proppant size of the proppant topromote shear fracturing in fractures of different size. In thiscontext, specifying the size comprises specifying the proppant size suchthat the proppant as sand enters fractures in the subterranean formationhaving a fracture width larger than the sand grains as measured bypassing the sand through sieves, the fractures including sand-filledshear fractures coupled to a natural diffusion flow fracture network ofa hydrocarbon reservoir in the subterranean formation.

The indicator may be received during the hydraulic fracturing. Theindicator may be correlative with volume of proppant placed in shearfractures generated in the shear fracturing.

The shear fractures generated in the shear fracturing may connect topores and natural fractures in the subterranean formation wherehydrocarbon moves by diffusion in natural fractures, wherein the naturalfractures include natural expulsion fractures that exhibit capillaryflow of hydrocarbon. The method include specifying size of the proppantsuch that proppant flows into the shear fractures and the naturalfractures, wherein the natural fractures have different sizes, andwherein the size of the proppant comprises 100 mesh or smaller sizesthat can enter into the shear fractures and natural fractures. Theproppant facilitates connecting of the shear fractures with the naturalfractures.

Lastly, embodiments of the present techniques may include hydraulicfracturing a subterranean formation including determining the amount ofcomplex shear fracturing that is occurring. The hydraulic fracturinginvolves injecting a frac slurry having frac fluid through a wellboreinto the subterranean formation, hydraulic fracturing the subterraneanformation with the frac slurry, and observing change in the amount ofhydraulic fracturing. The hydraulic fracturing includes complex shearfracturing the rock in the subterranean formation. Operating parametersof the hydraulic fracturing may be adjusted in real time to increase theamount of complex fracturing occurring per unit time. Such adjusting maybe based on resonant frequency at which the rock fractures. The fracturesurface area may be considered. The complex shear fracturing may assistwith diffusion production from areas of high hydrocarbon concentrations(reservoir source rocks) to areas with lower hydrocarbon concentrations(water-filled hydraulic fractures).

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the disclosure.

What is claimed is:
 1. A method comprising: receiving values of pressureas measured, the pressure associated with hydraulic fracturing of asubterranean formation with frac fluid injected through a wellbore intothe subterranean formation, the hydraulic fracturing comprising complexshear fracturing of the subterranean formation; determining an indicatorof the complex shear fracturing occurring per unit time, wherein theindicator is based on a Fourier transform of at least one of thepressure, pressure derivative, or pressure patterns; and specifyingadjusting an operating parameter of the hydraulic fracturing to increasethe complex shear fracturing, wherein the operating parameter comprisesflow rate of the frac fluid, fluid viscosity of the frac fluid, orproppant concentration in the frac fluid, or any combinations thereof,and wherein the hydraulic fracturing comprises adjusting the operatingparameter as specified.
 2. The method of claim 1, wherein the complexshear fracturing comprises connecting complex shear fractures generatedin the complex shear fracturing to natural fractures in the subterraneanformation.
 3. The method of claim 1, wherein the indicator iscorrelative with surface area of complex shear fractures generated inthe complex shear fracturing, wherein the pressure comprises wellheadpressure, downhole pressure, or a calculated pressure, or anycombinations thereof, and wherein the complex shear fracturing givesincreased production rate of hydrocarbon from the subterranean formationthrough the wellbore and gives increased hydrocarbon recovery from thesubterranean formation through the wellbore.
 4. The method of claim 1,wherein the pressure is measured via a pressure sensor at a wellhead ofthe wellbore or via a pressure sensor downhole in the wellbore, or acombination thereof, wherein the operating parameter comprises the flowrate of the frac fluid as injected, and wherein complex shear fracturesgenerated in the complex shear fracturing connect to natural fracturesthat exhibit capillary or diffusion flow of hydrocarbon.
 5. The methodof claim 1, wherein the indicator is based on stress patterns in rock inthe subterranean formation observed via the pressure as measured.
 6. Amethod, comprising: receiving values of pressure associated withhydraulic fracturing a subterranean formation with frac fluid pumpedthrough a wellbore into the subterranean formation, the hydraulicfracturing comprising complex shear fracturing rock in the subterraneanformation; determining an indicator of an amount of the complex shearfracturing, wherein the indicator is based on a Fourier transform of atleast one of the pressure, pressure derivative, or pressure patterns;and specifying adjusting an operating parameter of the hydraulicfracturing to increase the amount of the complex shear fracturing,wherein the operating parameter comprises flow rate of the frac fluid,fluid viscosity of the frac fluid, or proppant concentration in the fracfluid, or any combinations thereof, and wherein the hydraulic fracturingcomprises adjusting the operating parameter as specified.
 7. The methodof claim 6, wherein the complex shear fracturing comprises connecting tonatural fractures in the subterranean formation.
 8. The method of claim6, wherein the indicator of the amount of the complex shear fracturingcomprises an indicator of the amount of the complex shear fracturingoccurring per unit time.
 9. The method of claim 6, wherein the hydraulicfracturing triggers stress waves in the rock with the frac fluid,wherein the stress waves are self-propagating and compriseconstructively interfering stress waves that contribute to the complexshear fracturing, and wherein the operating parameter comprises the flowrate of the frac fluid as pumped.
 10. The method of claim 6, whereinproppant in the frac fluid facilitates transfer of pressure of the fracfluid to the rock as stress, and wherein the complex shear fracturinggives complex shear fractures that couple to existing natural fracturesin the subterranean formation, thereby resulting in increased diffusionrecovery of hydrocarbon from the subterranean formation through thewellbore.
 11. The method of claim 6, wherein the complex shearfracturing connects to natural fractures in the subterranean formation.12. The method of claim 6, wherein the pressure is measured in realtime, and wherein receiving the values of the pressure comprisesreceiving in real time the values of the pressure as measured.
 13. Themethod of claim 6, wherein the indicator of the amount of the complexshear fracturing is correlative with surface area of complex shearfractures generated in the complex shear fracturing.
 14. The method ofclaim 6, wherein the amount of the complex shear fracturing comprisessurface area of complex shear fractures generated in the complex shearfracturing, wherein the pressure is measured at a wellhead associatedwith the wellbore or downhole in the wellbore, or a combination thereof,and wherein adjusting the operating parameter as specified gives failurein the rock contributing to the complex shear fracturing.
 15. Ahydraulic fracturing system comprising: a control system to: receivemeasured pressure data of pressure associated with hydraulic fracturingof a subterranean formation in Earth crust with a frac fluid injected bythe hydraulic fracturing system through a wellbore into the subterraneanformation, the hydraulic fracturing comprising complex shear fracturingof the subterranean formation; determine an indicator of the complexshear fracturing occurring per unit time, wherein the indicator is basedon a Fourier transform of at least one of the pressure, pressurederivative, or pressure patterns; and adjust an operating parameter ofthe hydraulic fracturing to increase the complex shear fracturing,wherein the operating parameter comprises flow rate of the frac fluid,fluid viscosity of the frac fluid, or proppant concentration in the fracfluid, or any combinations thereof.
 16. The hydraulic fracturing systemof claim 15, wherein the indicator is correlative with surface area ofcomplex shear fractures generated in the complex shear fracturing, andwherein to adjust the operating parameter comprises specifying a setpoint of the operating parameter.
 17. The hydraulic fracturing system ofclaim 15, wherein to adjust the operating parameter comprises adjustingthe operating parameter of the hydraulic fracturing in real time, andwherein the hydraulic fracturing generates complex shear fractures andtensile fractures.
 18. The hydraulic fracturing system of claim 15,wherein the indicator is correlative with surface area of complex shearfractures generated in the complex shear fracturing, wherein themeasured pressure data is generated via measuring pressure at a wellheador downhole in the wellbore, or a combination thereof.
 19. A method,comprising: receiving values of pressure associated with hydraulicfracturing a subterranean formation with frac fluid pumped through awellbore into the subterranean formation, the hydraulic fracturingcomprising complex shear fracturing rock in the subterranean formation;receiving an indicator of an amount of the complex shear fracturing; andspecifying adjusting an operating parameter of the hydraulic fracturingto increase the amount of the complex shear fracturing, wherein theoperating parameter comprises flow rate of the frac fluid, fluidviscosity of the frac fluid, or proppant concentration in the fracfluid, or any combinations thereof, wherein the hydraulic fracturingcomprises adjusting the operating parameter as specified, wherein thehydraulic fracturing generates stress waves in the rock, and wherein themethod comprises goal seeking via specifying adjusting the operatingparameter for the stress waves to propagate at resonant stress frequencyof the rock.
 20. A hydraulic fracturing system comprising: a computingdevice configured to: receive measured pressure data associated withhydraulic fracturing of a subterranean formation in Earth crust with afrac fluid injected through a wellbore into the subterranean formation,the hydraulic fracturing comprising complex shear fracturing of thesubterranean formation; determine an indicator of the complex shearfracturing occurring per unit time; adjust an operating parameter of thehydraulic fracturing to increase the complex shear fracturing, whereinthe operating parameter comprises flow rate of the frac fluid, fluidviscosity of the frac fluid, or proppant concentration in the fracfluid, or any combinations thereof; perform goal seeking via adjustingthe operating parameter to increase the complex shear fracturinggenerates stress waves in rock of the subterranean formation; andinterpret the measured pressure data to evaluate the stress waves,wherein a goal of the goal seeking is the stress waves propagating atresonant stress frequency of the rock.